This paper proposes a new technical process to utilize
flue gas
desulfurization (FGD) gypsum in fluidized beds. Gypsum is stable in
the inert atmosphere and instable in the reducing atmosphere. Decomposing
properties of gypsum in multiatmospheres were investigated in both
a thermogravimetric analyzer (TGA) and a fluidized bed reactor. Results
from the TGA showed that the initial decomposing temperatures of gypsum
in all reducing atmospheres are about 800 °C; however, the ratio
between CaS and CaO in the product is influenced by CO concentration
([CO]). Higher [CO] is beneficial to speeding the decomposition. The
analysis of mass spectrometer showed that part of CaS was oxidized
to CaO when the atmosphere was changed from the reducing one with
[CO] = 2% to the oxidizing one with O2 concentration of
0.6%, which was proved by the XRD analysis of the final product with
content of CaO of 91.6%. Fluidized bed experiments were done in a
hot, lab scale, bubbling reactor. Results showed that CO2 can increase the CaO content in the product by restraining the side
production of CaS significantly. After gypsum decomposition in the
reducing atmosphere, a certain amount of air was injected to change
the atmosphere to oxidizing, and more SO2 was released.
The present research proves that a multistage fluidized bed system
with multiatmospheres is feasible for gypsum decomposition.